The present invention is directed to delivery of a glass stream for forming glass charges or gobs for glassware manufacture, and more particularly to a method and apparatus for delivering a so-called cased glass stream in which an inner or core glass is surrounded by an outer or casing glass.
It has heretofore been proposed in U.S. Pat. No. 4,740,401 to provide a cased glass stream for forming glassware having layered wall segments. U.S. Pat. Nos. 5,776,221 and 5,855,640 disclose techniques for delivering such a cased glass stream in which core glass from a first source is delivered through at least one first orifice. A second orifice is vertically spaced beneath and aligned with each first orifice, and is surrounded by a chamber that communicates with the second orifice through a gap between the first and second orifices. A heated tube delivers casing glass from a second glass source to the chamber that surrounds the second orifice. Glass flows by force of gravity through the orifices from the first and second sources in such a way that a cased glass stream emerges from the second orifice. This cased glass stream may be sheared by conventional techniques to form individual cased glass gobs for delivery to conventional individual section glassware forming machines.
Although the techniques disclosed in the noted patents address and overcome problems theretofore extant in the art, further improvements remain desirable. For example, in the systems disclosed in the noted patents, the lower orifice is formed by a metal bushing received in an opening in a ceramic lower orifice ring. The bushing has an upper flange that rests on a ceramic pedestal extending upwardly from the surface of the orifice ring, which effectively raises the flange above the surface of the ring. The flange on the bushing must be raised above the surface of the orifice ring because casing glass flows along this surface to the backside of the gap between the upper and lower orifices to form the layer around the core glass. However, it has been found that this pedestal of ceramic material erodes due to high temperature casing glass flow around the pedestal, eventually resulting in leakage of glass between the outer surface of the bushing and the surrounding ceramic material of the orifice ring. It is a general object of the present invention to provide a method and apparatus for delivering a cased glass stream in which the inlet end of the metal bushing is raised above the surface of the orifice ring to permit glass flow along the surface beneath the bushing, but which reduces erosion of the ceramic material and glass leakage between the bushing and the orifice ring opening.
Apparatus for forming a cased glass stream having an inner core glass surrounded by an outer casing glass, in accordance with one aspect of a presently preferred embodiment of the invention, includes a first or upper orifice ring having at least one orifice for receiving core glass, and a second or lower orifice ring secured beneath the first orifice ring and having a second orifice aligned with each first orifice. A chamber for receiving casing glass is formed between the first and second orifice rings surrounding the second orifice. A bushing is received in an opening in the second orifice ring to form each second orifice in the second orifice ring. The bushing has a first radially extending flange supported on an upper surface of the second orifice ring and a bushing end spaced upwardly from the first flange for admitting casing glass from the chamber to the second orifice. The first flange thus effectively spaces the bushing end above the surface of the second orifice ring, eliminating any need for the ceramic pedestal that can erode due to casing glass flow along the surface of the second orifice ring. The flange remains in firm facing abutment with the second orifice ring surface, reducing leakage of casing glass between the bushing and the opposing surface of the second orifice ring.
In the preferred embodiment of the invention, the second orifice ring is of ceramic construction, and the bushing is of metal construction. The bushing comprises a cylindrical body having the first flange secured between the ends of the body, and a second flange extending radially outwardly from an end of the bushing body spaced from the orifice ring surface. The opposing end of the bushing body extends through an opening in the orifice ring, and is secured to the orifice ring by means of a ferrule secured to the end of the bushing body. The undersurface of the orifice ring surrounding the bushing opening preferably is conically countersunk, and the ferrule has a conical surface in sliding engagement with the conically countersunk surface of the orifice ring. In this way, the ferrule remains in sealing abutment with the opposing countersunk surface of the orifice ring during thermal axial and radial expansion of the metal bushing as it is heated by flow of glass through the bushing.
In accordance with another aspect of the present invention, there is provided an orifice ring assembly for a cased glass apparatus, which includes a ceramic lower orifice ring having a pocket with a laterally extending passage for receiving casing glass, and at least one opening extending through the orifice ring from the pocket. A metal bushing is secured in each such opening. The bushing has a cylindrical body with opposed ends, a first flange extending from the bushing body between the ends in facing engagement with the opposing upper surface of the orifice ring pocket, and a second flange at one end of the bushing spaced from the pocket surface. The other end of the bushing is disposed adjacent to an undersurface of the orifice ring, and a ferrule is secured to such other end in facing abutment with the undersurface. The orifice ring undersurface preferably has a conical countersunk portion surrounding each opening, and each ferrule has a conical surface in facing abutment with the conical countersunk portion for maintaining facing abutment with the conical countersunk surface portion during thermal expansion of the bushing.